Infectious disease research has focused on the role of prokaryotic surface molecules or adhesions which mediate attachment and colonization (15). Adhesions are considered major virulence determinants of microorganisms because these molecules play a key role in attachment and colonization of pathogenic bacteria (34) . Periodontitis is a mixed microbial infection and adhesive interactions in the form of bacterial cell to cell heterotypic binding has been observed morphologically in dental plaque (24). However, little is known of the role of these interactions in the pathogenesis of human periodontal disease. We have investigated aggregation between Capnocytophaga gingivalis, a gram- negative oral bacterium, and the gram-positive oral bacterium Actinomyces israelii. Using aggregation inhibiting Mabs, we were able to identify a 140-155 kD non-fibrial associated adhesion (NFA140) (42). Using monospecific polyclonal antiserum, we identified a recombinant with a 4.2 kb C. gingivalis genomic DNA fragment which rendered transformed E. coli capable of aggregating with A. israelii. Objective of this proposal is to provide detailed molecular and immunological information regarding NFA140. The information generated by the work proposed here will provide information about an oral bacterial adhesion and will formulate the basis for further much needed work in this area of periodontal research. Our Specific Aims are to: 1. Obtain DNA base sequence, detailed restriction map, deduced amino acid sequence and identify coding regions of the 4.2 kb C. gingivalis DNA fragment and the NFA140 gene. 2. Determine the prevalence of C. gingivalis recent isolates showing A. israelii-specific aggregation inhibited by adhesion-specific Mabs 1AA4 and 2AD5. Determine the association of the aggregation phenotype with the presence of complimentary DNA and RNA in aggregation positive and negative C. gingivalis strains using an adhesion-specific DNA probe. 3. Determine IgG serum reactivity to C. gingivalis OM and NFA140 of juveniles and adults harboring the microorganism using Western blot and enzyme-linked immunosorbent assay. In addition, determine the prevalence of NFA140 in plaque samples of young humans using indirect immunofluorescence.